Source of interest in London, for example (7)
I believe the answer is:
capital
This clue might be a double definition.
'source of interest' is the first definition.
'capital' can be an answer for 'source' (I have seen 'source of profit' mean 'capital' so perhaps 'source' could also mean 'capital'). I am not sure about the 'of interest' bit.
'london for example' is the second definition.
(London is an example)
'in' acts as a link.
Can you help me to learn more?
(Other definitions for capital that I've seen before include "Seed money" , "City - finance - very good" , "source of profit" , "Money saved or invested - seat of government" , "Cardiff, say" .)